Referring to FIGS. 9 to 11 or Taiwan Patent No. M339956, a conventional adjustable table (40) comprises a leg portion (41), a locating seat (42), a pivot base (43), a spring (44), a lever (45) and a tabletop (46). An outer tube (411) upwardly extends from a central portion of the leg portion (41), and am inner tube (412) is configured to be inserted into the outer tube (411) and have vertical movements relative to the outer tube (411). Moreover, a first pivot hole (413) is adapted to penetrate through an upper portion of the inner tube (412). The locating seat (42) and the pivot base (43) are respectively formed in an inverted-U shape, and two second pivot holes (421) respectively penetrate through two lateral surfaces of the locating seat (42) at corresponding positions while two third pivot holes (431) respectively penetrate through two lateral surfaces of the pivot base (43) at corresponding positions. After the locating seat (42) connected to the upper portion of the inner tube (412), the locating seat (42) is configured to be mounted on the pivot base (43) to align the third pivot holes (431) with the second pivot holes (421) and the first pivot hole (413), and a shaft is adapted to penetrate through the first pivot hole (413), the second pivot holes (421) and the third pivot holes (431) to secure the pivot base (43) with the locating seat (42) and the inner tube (412). Furthermore, a locating hole (422) and an arc-shaped guiding groove (423) are respectively formed at one of the lateral surfaces of the locating seat (42), and a row of blocking holes having a larger diameter than the guiding groove (423) are sequentially formed on the guiding groove (423). The lateral surface of the pivot base (43), which is located on the same side of the guiding groove (423), is connected to a connecting portion (432), and two lateral surface of the connecting portion (432) which are respectively close to and away from the pivot bae (43) respectively comprise a hollow rib (434) and an opening (433), and a side groove communicated with the opening (433) is formed at a rear surface of the connecting portion (432) which is perpendicular to the two lateral surface. Additionally, the pivot base (43) is configured to be secured on the tabletop (46). The lever (45) has a hook-shaped pulling portion (451) and a head end (453) respectively formed at two ends thereof, and a bent extending portion (432) is formed between the pulling portion (451) and the head end (453). The tabletop (46) has a through hole (461) located at a side of a bottom surface thereof, and the head end (453) is adapted to pass through the through hole (461) to extend along the bottom surface of the tabletop (46). The spring (44) is adapted to be coupled in the side groove of the connecting portion (432), and the head end (453) is configured to pass through the spring (44). Also, a bolt (47) located adjacent to the head end (453) is adapted to penetrate through the lever (45) to couple with the spring (44) such that when the lever (45) is pulled, the bolt (47) is configured to compress the spring (44).
When the tabletop (46) is horizontal, the hollow rib (434) of the pivot base (43) is configured to align with a lowest one of the blocking holes (424), and the protruding head end (453) is adapted to engage with the blocking hole (424), thereby securing the tabletop (46) at a horizontal position through the spring (44). When the use angle of the tabletop (46) needs to be changed, a user can pull the pulling portion (451) of the lever (45) outwardly to move the head end (453) inwardly (as shown in FIG. 12), and the spring (44) is adapted to be compressed by the bolt (47) such that the head end (453) can be detached from the blocking hole (424), and then the tabletop (46) can be flipped with an angle. Meanwhile, the pivot base (43) is pivotally rotated about the guiding groove (423), and when the lever (45) is released, the spring (44) is configured to move the lever (45) back to an initial position, thereby engaging the head end (453) in a different blocking hole (424). With the fore-mentioned structures, a user can complete adjusting the angle of the tabletop (46) with one hand. On the contrary, when the tabletop (46) needs to be folded, a user can pull out the lever (45) and flip the tabletop downward, and thereafter a user can align the hollow rib (434) of the pivot base (43) with the locating hole (422) of the locating seat (42), and then release the lever (45) such that the head end (453) is adapted to engage in the locating hole (422), thereby securing the tabletop (46) in a folded position.
However, the conventional adjustable table is disadvantageous because: (i) the lever (45) only can engage on a single lateral side of the pivot base (43), and when another lateral side of the pivot base (43) is pressed, the pivot base (43) is configured to misalign with the locating seat (42), leading to the unstableness of the tabletop (46); and (ii) it needs a lot of efforts for a user to adjust the angle of the tabletop (46) in a manner of pulling the lever (45). Therefore, there remains a need for a new and improved design for an adjustable table to overcome the problems presented above.